1. Field of the Disclosure
The present disclosure relates generally to a system of couplings or connectors and method of use of the couplings with a downhole tool for use in oil and gas wells, and more specifically, to a ported completion in combination with a system of couplings and a bottom hole assembly that can be employed for fracturing in multi-zone wells.
2. Description of the Related Art
Oil and gas well completions are commonly performed after drilling hydrocarbon producing wellholes. Part of the completion process includes running a well casing assembly into the well. The casing assembly can include multiple lengths of tubular casing attached together by collars. A standard collar can be, for example, a relatively short tubular or ring structure with female threads at either end for attaching to male threaded ends of the lengths of casing. The well casing assembly can be set in the wellhole by various techniques. One such technique includes filling the annular space between the wellhole and the outer diameter of the casing with cement.
After the casing is set in the well hole, perforating and fracturing operations can be carried out. Generally, perforating involves forming openings through the well casing and into the formation by commonly known devices such as a perforating gun or a sand jet perforator. Thereafter, the perforated zone may be hydraulically isolated and fracturing operations are performed to increase the size of the initially-formed openings in the formation. Proppant materials are introduced into the enlarged openings in an effort to prevent the openings from closing.
More recently, techniques have been developed whereby perforating and fracturing operations are performed with a coiled tubing string. One such technique is known as the Annular Coil Tubing Fracturing Process, or the ACT-Frac Process for short, disclosed in U.S. Pat. Nos. 6,474,419, 6,394,184, 6,957,701, and 6,520,255, each of which is hereby incorporated by reference in its entirety. To practice the techniques described in the aforementioned patents, the work string, which includes a bottom hole assembly (“BHA”), generally remains in the well bore during the fracturing operation(s).
One method of perforating, known as the sand jet perforating procedure, involves using a sand slurry to blast holes through the casing, the cement and into the well formation. Then fracturing can occur through the holes. One of the issues with sand jet perforating is that sand from the perforating process can be left in the well bore annulus and can potentially interfere with the fracturing process. Therefore, in some cases it may be desirable to clean the sand out of the well bore, which can be a lengthy process taking one or more hours per production zone in the well. Another issue with sand jet perforating is that more fluid is consumed to cut the perforations and either circulate the excess solid from the well or pump the sand jet perforating fluid and sand into the zone ahead of and during the fracture treatment. Demand in industry is going toward more and more zones in multi-zone wells, and some horizontal type wells may have 40 zones or more. Cleaning the sand from such a large number of zones can add significant processing time, require the excessive use of fluids, and increase the cost. The excessive use of fluids may also create environmental concerns. For example, the process requires more trucking, tankage, and heating and additionally, these same requirements are necessary when the fluid is recovered from the well.
Well completion techniques that do not involve perforating are known in the art. One such technique is known as ball drop open hole style completion. Instead of cementing the completion in, this technique involves running open hole packers into the well hole to set the casing assembly. The casing assembly includes ported collars with sleeves. After the casing is set in the well, the ports can be opened by operating the sliding sleeves. Fracturing can then be performed through the ports.
For multi-zone wells, multiple ported collars in combination with sliding sleeve assemblies have been employed. The sliding sleeves are installed on the inner diameter of the casing and/or sleeves and can be held in place by shear pins. In some designs, the bottom most sleeve is capable of being opened hydraulically by applying a differential pressure to the sleeve assembly. After the casing with ported collars is installed, a fracturing process is performed on the bottom most zone of the well. This process may include hydraulically sliding sleeves in the first zone to open ports and then pumping the fracturing fluid into the formation through the open ports of the first zone. After fracturing the first zone, a ball is dropped down the well. The ball hits the next sleeve up from the first fractured zone in the well and thereby opens ports for fracturing the second zone. After fracturing the second zone, a second ball, which is slightly larger than the first ball, is dropped to open the ports for fracturing the third zone. This process is repeated using incrementally larger balls to open the ports in each consecutively higher zone in the well until all the zones have been fractured. However, because the well diameter is limited in size and the ball sizes are typically increased in quarter inch increments, this process is limited to fracturing only about 11 or 12 zones in a well before ball sizes run out. In addition, the use of the sliding sleeve assemblies and the packers to set the well casing in this method can be costly. Further, the sliding sleeve assemblies and balls can significantly reduce the inner diameter of the casing, which is often undesirable. After the fracture stimulation treatment is complete, it is often necessary to mill out the balls and ball seats from the casing.
Another method that has been employed in open-hole wells (that use packers to fix the casing in the well) is similar to the ball drop open hole style completion described above, except that instead of dropping balls to open ports, the sleeves of the subassemblies are configured to be opened mechanically. For example, a shifting tool can be employed to open and close the sleeves for fracturing and/or other desired purposes. As in the case of the completion, the sliding sleeve assemblies and the packers to set the well casing in this method can be costly. Further, the sliding sleeve assemblies can undesirably reduce the inner diameter of the casing. In addition, the sleeves are prone to failure due to high velocity sand slurry erosion and/or sand interfering with the mechanisms.
Another technique for fracturing wells without perforating is disclosed in co-pending U.S. patent application Ser. No. 12/826,372 entitled “JOINT OR COUPLING DEVICE INCORPORATING A MECHANICALLY-INDUCED WEAK POINT AND METHOD OF USE,” filed Jun. 29, 2010, by Lyle E. Laun, which is incorporated by reference herein in its entirety.
Other techniques for fracturing wells without perforating are disclosed in co-pending U.S. patent application Ser. No. 12/842,099 entitled “BOTTOM HOLE ASSEMBLY WITH PORTED COMPLETION AND METHODS OF FRACTURING THEREWITH,” filed Jul. 23, 2010 by John Edward Ravensbergen and Lyle Laun, and Ser. No. 12/971,932 entitled “MULTI-ZONE FRACTURING COMPLETION,” filed Dec. 17, 2010 by John Edward Ravensbergen, both which are incorporated by referenced herein in its entirety.
One potential problem with using coiled tubing in a horizontal well is accurately positioning a BHA at a desired location within the well so that the BHA is adjacent to a fracture port permitting communication to the zone to be fractured and/or treated. While moving a BHA up the casing, coiled tubing operators often rely on a tally sheet that indicates the length of casing segments or tubulars that have been inserted into the well. Coiled tubing operators generally run a BHA on coiled tubing to the bottom of the well and then pull the coiled tubing up the casing using the tally sheet to indicate casing joints, couplings, or connections along the casing tubular string. As the BHA is pulled up the string a casing collar locator (“CCL”) is used to help determine the location of the BHA. As is known by one of ordinary skill in the art, a mechanical CCL engages a locating profile on joints or connections between casing or tubular segments, which requires the operator to increase the pull out of hole force as the CCL passes through each connection as the BHA is moved up the well.
The operator uses the tally sheet in combination with pulling the CCL through each connector to determine the actual location of the BHA. However during the installation of the casing or tubing, the depths recorded on the tally sheet may not be accurate. For example, upon creating the tally sheet an incorrect length for a tubular or casing segment may be recorded leading to an inaccurate determination of the current position of the BHA. The operator may encounter a joint earlier than expected causing the operator to stop the process to determine the actual location of the BHA. Each such determination can add additional hours to the overall time required for the multi-zone treatment and/or stimulation process. A well may typically have 15-20 zones to be treated and/or stimulated. The problem of having an incorrect tally sheet for locating one zone can be problematic when locating the following zones during the process. Having problems locating multiple zones during the treatment and/or stimulation process can add a large number of hours and thus, expense to the operation. Thus, it would be beneficial to improve the confidence in properly locating the BHA with a failure rate that is at least 1 out of 50 or even better than 1 out of 100 to potential minimize the overall cost of the operation.
Additionally, the coiled tubing operator may sense false indications at the surface creating additional confusion as to the actual location of the BHA. A false indication is caused by an increase in the pull out of hole (POOH) force without the CCL engaging a collar profile. False indications may be caused by several factors. The POOH force is a function of the contact forces along the length of the coiled tubing and the coefficient of friction. In a horizontal well only a portion of the coiled tubing is in contact with the well casing, due to the helical or curved shapes of the coiled tubing and the well bore. Therefore the false indication created by the variations in POOH may be caused by these geometrical differences, and/or the difference between static and dynamic coefficients of friction. The POOH force is typically greater than the force required to pull the CCL through a collar profile and therefore the variations are large enough to create false indications. In addition, sand within the horizontal well introduces yet another variable that may interfere with movement of the BHA and potentially leading to false indications at the surface.
One potential way to limit false positives would be to increase the POOH force require to pull the CCL through a collar profile by increasing the force of the spring loaded dogs on the CCL. However, as the force of the spring loaded dogs are increase the required pushing force to run into the hole (RIH) also increases. Presently, it can be difficult to push the BHA with the CCL to the bottom of a horizontal well with coiled tubing due to the limited pushing capacity of the coiled tubing. A larger diameter of coiled tubing could possibly be used to increase the pushing capacity, but the use of a larger diameter of coiled tubing would also present a greater expense.
The stimulation and/or treating of multiple zones within a well is a time consuming and costly operation. The time required to stimulate the specified multiple zones potentially increases if the operator repeatedly needs to take additional time to determine the actual location of a BHA rather than being able to move directly to each zone and perform the stimulation and/or treatment. Thus, it would be beneficial to provide a system and/or method that increases the efficiency of moving and locating a BHA within each zone to be stimulated and/or treated.
The present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.